May 1954 E-878
STATE PLANT BOARD
United States Department of Agriculture
Agricultural Research Service
Entomology Research Branch
SCREENING PROCEDURE FOR CANDIDATE FUMIGANTS
FOR STORED GRAIN AND GRAIN PRODUCTS
By N. M. Dennis and W. K. Whitney, Stored-Product Insects Section,
Biological Sciences Branch, Agricultural Marketing Service
Each year many new chemicals are submitted to the Manhattan,
Kans., station for testing as fumigants for stored grain and grain prod-
ucts. It would be impractical and unwise to conduct large-scale tests
with every compound so submitted for screening. The screening pro-
cedure described herein is designed to establish the minimum lethal
dosage of the candidate compounds, both in space and in commodities,
and their performance under various conditions. By this procedure a
candidate fumigant can be evaluated in the laboratory at normal atmos-
pheric pressure.
By use of this procedure not only may promising new fumigants be
discovered, but dosages may be established for large-scale tests in
warehouses and other storage facilities.
Before tests are started to evaluate the candidate compound, its
physical and chemical properties are reviewed. Many compounds may
be eliminated because of objectionable odor, flammability, corrosive-
ness to metal, deleterious effect on the viability of seed grain, or other
objectionable properties. Also its toxicity to man is considered, and
any necessary precautions in handling the fumigant are observed.
Germination tests are conducted if the compound shows promise as a
fumigant.
The confused flour beetle ( Tribolium confusum Duv.) and the rice
weevil ( Sitophilus oryza (L.)) are used to determine the comparative
toxicity of the fumigant being studied, as these species represent, re-
spectively, the more resistant and susceptible types of insects infesting
stored grain.
It is essential to have the condition and age of the test insects as
nearly uniform as possible. To provide a continuing supply, cultures
are started at weekly intervals. The insects are reared in a uniform
food medium under constant temperature (80° F.) and humidity (70 per-
cent), and tested as adults.
ass flasks and in empty glass
fumigant's , and then in
mmod. - . Before being exposes
s are places -mesh screen cages
.30 insects to a cage. The
cag< s impregnated with h' affin to prevent
the insects from boring into the
ks.
The fui tit is first tested in a 20-liter flask ( \ glass tube
through rubber s' • d to a glass stopcock out-
!-:. I wo cages, containing insects h species separate ,
of the flask. uum (about 20
the flask to 'ate introdu< • the nt.
f liquid fumigant in a pipette is then held over the
end of the glass tube ling from th« k, and n.-
aing t: - i : allowing the vacuum to draw the fumi. to
of 20 hours the insects are ex 1 for
. As : k on possible recovery a sec ond ob
made 5 days later. I n 3 to 5 rep! re
mtil thi ethal dosage is determined.
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and 6 feet higVis used (t.. . J . sts oT 1 foot
in 901 r %' ' sed
h disks o: . M Ir^rTirnMed with paraffi . ;es
• lining the test insects are su
Is — 1 in m the n ., u ter, md 1 inrh from the top.
A ; ^s-sampling tube is p. reside eacl to
M isonite disk. Thr.
hole in this disk 'lie Liquid fumig nl
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cylinders. In this way the minimum lethal dosage and the dispersion
of the gas may be determined, and also the time required for aeration
of a product after fumigation.
All the fumigation tests are conducted in a room where a tempera-
ture of 80° F. is thermostatically maintained. Small variations of the
temperature during the exposure period are recorded, but usually they
do not appreciably influence the results.
Figure 1. --Wire-screen cages for the test insects.
Figure 2.--A 20-liter flask with stopcock and sus-
pended test cages. The amount of vacuum in the
flask is being checked with a manometer prior to
the introduction of a measured amount of fumigant.
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